From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Subject: idr: fix overflow bug during maximum ID calculation at maximum height
idr_replace() open-codes the logic to calculate the maximum valid ID given
the height of the idr tree; unfortunately, the open-coded logic doesn't
account for the fact that the top layer may have unused slots and
over-shifts the limit to zero when the tree is at its maximum height.
The following test code shows it fails to replace the value for
id=((1<<27)+42):
static void test5(void)
{
int id;
DEFINE_IDR(test_idr);
#define TEST5_START ((1<<27)+42) /* use the highest layer */
printk(KERN_INFO "Start test5\n");
id = idr_alloc(&test_idr, (void *)1, TEST5_START, 0, GFP_KERNEL);
BUG_ON(id != TEST5_START);
TEST_BUG_ON(idr_replace(&test_idr, (void *)2, TEST5_START) != (void *)1);
idr_destroy(&test_idr);
printk(KERN_INFO "End of test5\n");
}
Fix the bug by using idr_max() which correctly takes into account the
maximum allowed shift.
sub_alloc() shares the same problem and may incorrectly fail with -EAGAIN;
however, this bug doesn't affect correct operation because
idr_get_empty_slot(), which already uses idr_max(), retries with the
increased @id in such cases.
[tj@xxxxxxxxxx: Updated patch description.]
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/idr.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff -puN lib/idr.c~idr-fix-overflow-bug-during-maximum-id-calculation-at-maximum-height lib/idr.c
--- a/lib/idr.c~idr-fix-overflow-bug-during-maximum-id-calculation-at-maximum-height
+++ a/lib/idr.c
@@ -249,7 +249,7 @@ static int sub_alloc(struct idr *idp, in
id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;
/* if already at the top layer, we need to grow */
- if (id >= 1 << (idp->layers * IDR_BITS)) {
+ if (id > idr_max(idp->layers)) {
*starting_id = id;
return -EAGAIN;
}
@@ -811,12 +811,10 @@ void *idr_replace(struct idr *idp, void
if (!p)
return ERR_PTR(-EINVAL);
- n = (p->layer+1) * IDR_BITS;
-
- if (id >= (1 << n))
+ if (id > idr_max(p->layer + 1))
return ERR_PTR(-EINVAL);
- n -= IDR_BITS;
+ n = p->layer * IDR_BITS;
while ((n > 0) && p) {
p = p->ary[(id >> n) & IDR_MASK];
n -= IDR_BITS;
_
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